"So, coral bleaching acts as a visual indicator of ocean warming. When corals are stressed by temperature changes, as well as changes in amount of light or nutrients, they expel the symbiotic algae that live in their tissues, which causes them to turn completely white or pale. Without the algae in their tissues, coral loses its major source of food and is more susceptible to disease. Coral can bounce back from small amounts of bleaching, but long-term bleaching is often deadly."
CREDIT: AP PHOTO/BEN CURTIS